1. Field of the Invention
The present invention relates to a piezoelectric ceramics and a manufacturing method therefore, and more particularly, to a lead-free piezoelectric ceramics. The present invention also relates to a piezoelectric element, a liquid discharge head, a liquid discharge apparatus, an ultrasonic motor, an optical apparatus, a vibration generator, a dust removing device, an imaging apparatus, and an electronic apparatus, which use the piezoelectric ceramics.
2. Description of the Related Art
A commonly used piezoelectric ceramics is an ABO3-type perovskite metal oxide such as lead zirconate titanate (hereinafter, referred to as “PZT”). However, it is considered that PZT, which contains lead as an A-site element, may cause environmental problems. Therefore, a piezoelectric ceramics with a lead-free perovskite-type metal oxide has been desired.
Barium titanate is known as a piezoelectric ceramics with a lead-free perovskite-type metal oxide. Japanese Patent Application Laid-Open No. 2008-150247 discloses barium titanate prepared by a resistance heating/two-step sintering technique. Japanese Patent Application Laid-Open No. 2008-150247 describes that ceramics with excellent piezoelectric property can be obtained when nano-sized barium titanate powder is sintered by the two-step sintering technique. However, barium titanate has a problem in that depolarization is caused by continuous driving of a device at high temperature (for example, 80° C. or more) because its Curie temperature is low at 125° C. In addition, because barium titanate has a structural phase transition temperature between orthorhombic and tetragonal at a temperature close to a room temperature, barium titanate has a problem in that its performance at a practical temperature becomes unstable.
In addition, “Journal of Applied Physics” 2008, Volume 87, Issue 2, pp. 855-862 discloses a solid solution of barium titanate and bismuth ferrite as an attempt to increase the Curie temperature of barium titanate. However, as the solid solution amount of the bismuth ferrite increases, the Curie temperature increases while a piezoelectric constant is conspicuously decreased.
In other words, it is difficult to achieve both high piezoelectric performance and a high Curie temperature in a piezoelectric ceramics of the lead-free perovskite-type metal oxide.